An organic light emitting diode display is a self-emission display device that has an organic light emitting diode that emits light to display an image. Since the organic light emitting diode display does not require a separate light source, unlike a liquid crystal display, it is possible to reduce thickness and weight thereof. Further, since the organic light emitting diode display has high-grade characteristics, such as low power consumption, high luminance, and a high response speed, the organic light emitting diode display receives attention as the next-generation display device for portable electronic apparatuses.
In the organic light emitting diode display, various efforts for reducing power consumption and increasing efficiency have been attempted. For example, there are examples to achieve low voltage, high efficiency, and long lifespan by using a material having high charge mobility in a hole injection layer, a hole transport layer, and the like.
FIG. 1 schematically illustrates a structure of a general organic light emitting diode. Referring to FIG. 1, in the general organic light emitting diode display, a first pixel electrode, a second pixel electrode, and a third pixel electrode as a first electrode 20 are formed on a substrate 10, and the first electrode 20 is partitioned by a pixel defining layer (PDL) 30 for each pixel unit. A light-emitting layer 50 is formed on the first electrode 20, and is classified into a red light-emitting layer, a green light-emitting layer, and a blue light-emitting layer, respectively. A common electrode as a second electrode 60 is formed on the light-emitting layer 50. At least one of a hole injection layer 42 and a hole transport layer 44 may be disposed between the first electrode 20 and the light-emitting layer 50. Further, at least one of an electron transfer layer 46 and an electron injection layer 48 may be disposed between the light-emitting layer 50 and the second electrode 60.
The light-emitting layer 50 is formed by selecting and applying a material capable of yielding maximum, or suitable, efficiency for each of the red light-emitting layer, the green light-emitting layer, and the blue light-emitting layer. Further, resistance for each of red, green, and blue light-emitting layers, and therefore, each driving voltage as well, varies according to the selected emission material. Accordingly, current is further concentrated in a pixel having low resistance (that is, low driving voltage) among red, green, and blue according to a physical property of current having a tendency to flow to a place having low resistance. However, in the process, when a color having the lowest resistance among red, green, and blue has highest emission efficiency, luminance in the entire panel is increased at black current, and a contrast ratio is deteriorated.